The major aim of these studies is to analyze and modify currently available models of chemical hepatocarcinogenesis, as well as to extend new models which we have developed; and, to delineate obligate components in the sequence of alterations which result in the appearance of carcinomas. To accomplish this purpose, we will examine the phenomena of synergism between carcinogens; the mechanism of sensitization of carcinogen-action which results from cell division; and, the influence on carcinogenic progression of a number of non-carcinogenic chemical and nutritional factors. For these purposes, we will utilize carcinogens which differ as to chemical class and differ in their mode of interaction at the molecular level. To determine the sequence of alterations thus induced, we will use a group of "markers" which include histochemistry (morphologic), alpha fetoprotein (biologic) and alkaline elution gradients (biochemical). The histochemical markers will include the enzyme gamma-glutamyl transpeptidase, a membrane enzyme which demonstrates early alteration during carcinogen exposure; iron uptake under conditions of iron overload; and, a "new marker," nile blue sulphate which stains for accumulation of fatty acids. Circulating alpha fetoprotein will be followed as a re-expression of fetal function which has been demonstrated to be associated with various cell populations during carcinogenesis. Alkaline elution gradients will be utilized to examine alterations in the DNA of target cells. The use of these measurements will also be aimed at determining if alterations of differing type are independent or coordinated.